This nonprovisional patent application claims priority upon Swedish Patent Application No. 0104260-5, filed on Dec. 17, 2001, the entire contents of which are herein incorporated by reference.
The present invention relates to a microwave heating system for heating voluminous elongated loads and a method in the system according to the preambles of the independent claims.
The primary area of the invention is large microwave applicators for treatment of large loads with typically lower permittivities than those of compact items with high water content. In particular, the invention relates to tank systems with over- or underpressure in which the load is located. Such systems will typically consist of thick wall pressure tanks with circular cross section and provisions for load insertion and removal through solid heavy doors at one or both ends.
However, the person skilled in the art of microwave heating appreciates that the invention is equally applicable for treatment of smaller loads using an appropriately sized microwave cavity volume.
A microwave heating system is known, from e.g. U.S. Pat. No. 4,045,639 that discloses a system used mainly for microwave drying of delicate food substances with under-pressure in a tank. However, no particular provisions for creating particular or desirable mode patterns are addressedxe2x80x94multimode cavity characteristics are used, and the microwave feeding is performed through microwave transparent windows using known rectangular TE1;0 waveguides or even larger windows.
A particular problem with pressurised microwave applicators concerns the need for a seal of the microwave feed-through device that does not leak air/gas or liquid. In particular, common types of waveguide windows with conventional seals cannot be used when corrosive media exist and participate in the chemical processing in the tank, and when there is a significant difference between its pressure and that of the ambient. The problems are exacerbated with high temperatures and temperature cycling.
Using coaxial line feed-through provisions will reduce the problems with sealing of the periphery as well as allow smaller cross section dimensions so that the mechanical strength of the tank is improved, in comparison with the use of state-of-the art microwave windows. However, the electric field intensity is highest at the centre conductor, which together with the normally unavoidable resistive losses in this conductor may result in a quite low power handling capability.
The object of the present invention is to achieve a microwave heating system where the heating pattern inside a cavity is easier to control and predict. Still another object is to achieve a microwave heating system especially adapted for treatment of voluminous elongated loads.
The above-mentioned objects are achieved by the present invention according to the independent claims.
Preferred embodiments are set forth in the dependent claims.
Thus, the present invention relates to a microwave heating system especially adapted for heating voluminous elongated loads arranged in a cavity where a heating pattern persists, caused by a cavity single mode.